2.2 Cavity and Batten Installation
Drained and ventilated cavities are seen as one way of dealing with moisture that may enter through the exterior envelope. Resene Construction Systems recommends the use of cavities.
When a drainage cavity is used, it should consist of an air space outboard of a building underlay fixed to the framing, with approved flashings to drain water to the outside face of the cladding.
2.5.2. Batten Types
Polystyrene cavity battens
Use expanded polystyrene Class H or extruded polystyrene (for more information, refer to E2/AS1 Paragraph 18.104.22.168). Vapour from freshly LOSP-treated timber may melt polystyrene battens.
Timber cavity battens
Use radiata cavity battens of merchantable grade that are treated to a minimum of H3.2. Do not rip battens from larger members, as untreated timber may be exposed. Most cavity battens are treated using LOSP treatment.
- wall underlay refer to E2/AS1 Table 23
- factory painting of the metal cladding (except in ‘sea spray’ and ‘zone 1’
- corrosion zones – refer to E2/AS1 Table 21
Cavibat (plastic battens) , and James Hardie CLD structural battens are also suitable options. Please refer to manufacturers specifications for their uses and installation instructions.
For more information on creating a structural batten refer to BRANZ Bulletin # 475 of August 2006 "Structurally Fixing Battens for Horizontal Weatherboards"
2.5.3. Fixing Battens
There are several ways in which a polystyrene batten can be fixed.
Adhesive fixing to the building underlay. This is probably the quickest method of fixing battens. The adhesive acts as a temporary fixing, and it will be permanently fixed upon nailing the substrate in place. Under no circumstances should any solvent-based adhesives be used, as these will melt the polystyrene battens.
Nail Fixing of Polystyrene battens or Timber battens, slower than the other methods but just as effective. When nail fixing a batten drive the nail on a slight angle to gain a better grip to the structure. If you are using a Framing Nail Gun to fix your battens use a 75mm nail and fix at no greater than 300 centres. If you are nailing by hand use a Galvanised Flathead Ringshank nail.
Remember the battens only need to be temporarily held in place, for when you fix the substrate at the appropriate centres this will secure all the battens in place.
Support for vertical fixings
For more information on nail penetrations with particular claddings, refer to E2/AS1 Table 24.
Fix vertical battens on stud lines. Vertical battening must be the full height of the cavity, but battens may be joined (butted) to achieve this.
Take account of where cladding fixings will be needed for the exact location of the battens. For example, at corners or cladding junctions, provide additional or wider battens as required for fixing the cladding, back-flashings or facings.
Support for horizontal fixings
Where an intermediate or horizontal fixing is required, for example to fix the top or bottom edge of sheet cladding, install a cavity spacer (short length of batten) on a minimum 5° slope. Leave a minimum 50 mm gap between the spacer and the vertical battens (the gap is to provide drainage and ventilation)
Closing off the top of the cavity
Ventilation is not required at the top of a cavity (note that masonry veneer uses a different cavity system that does require top venting)
Close off the top of the cavity to prevent damp air from the cavity getting into interior spaces, roof framing or eaves. This is particularly important where the cavity finishes beneath a soffit or other area that might be open to a roof space.
One way of closing off the top of the cavity is to use a continuous length of horizontal batten as shown in Figure 9. The horizontal batten also supports fixings at the top edge of sheet claddings where required.
Cavity walls over two storeys
Refer to E2/AS1 Paragraph 22.214.171.124
Cavities may be continuous up to two storeys or 7m maximum but not more, due to limits on drainage and drying. If the wall is greater than two storeys or 7m, divide the cavity using a horizontal flashing that bridges the cavity. Provide ventilation to the cavity above the junction, as described for the base of the wall.
It is the builder’s responsibility for the supply and installation of the horizontal flashing according to E2/AS1.
Existing Substrates – over timber framing
Generally deals with existing weatherboard or rigid backing boards (fibre cement sheet)
Battens must be screw fixed to ensure positive fixing through to the structural framing.
Screw fixing of battens is recommended as existing internal linings may be damaged if nails are hammered into the structural framing.
Solid Filled Masonry / ICF Substrate – timber battens
Generally deals with solid filled concrete block, precast panels, & ICF (polystyrene blocks)
Timber battens must be mechanically fixed to ensure positive fixing through to the concrete substrate.
The cladding must be screw fixed tight against the timber battens.
Timber battens are used in this situation as they provide adequate support for subsequent screw fixed cladding installation.
Solid Filled Masonry Substrate – polystyrene battens
If polystyrene battens are used they must be tacked to the concrete substrate.
The cladding must be fixed with appropriate IDP fasteners through the polystyrene batten and into the concrete substrate.